Compressed-gas circuit interrupter



y 6 E. GISIGER 3,253,107

COMPRESSED-GAS CIRCUIT INTERRUPTER Filed May 6, 1963 Fig. l.

LOW PRESSURE HIGH PRESSURE CLOSE 52 IIO ' WITNESSESI INVENTOR Ernst Gisiger a? 6 w j gg I United States Patent 3,253,107 COMPRESSED-GAS CIRCUIT INTERRUPTER Ernst Gisiger, Zurich, Switzerland, assignor to Siemens- Schuckertwerke Aktiengesellschaft, Erlangen, Germany, a corporation of Germany Filed May 6, 1963, Ser. No. 278,041 Claims priority, application Germany, May 7, 1962,

6 Claims. or. 200-148) This invention relates generally to compressed-gas circuit interrupters and, more particularly, to compressedgas circuit interrupters of the type in which outlet-valve means for a high-pressure chamber are utilized and opened during the arc-extinguishing operation. The invention has particular applicability to synchronous-type com pressed-gas circuit interrupters in which the separable contacts are opened on the descending portion of the alternating-current wave, say, for example, approximately 2 milliseconds prior to a current zero with relation to a SO-cycle-per-second frequency. The present invention is not exclusively, however, limited in application to such types of compressed-gas interrupters but may be applied to other types.

A general object of the present invention is to provide an improved and highly efficient outlet-valve operating arrangement to minimize the consumption of the arc-extinguishing gas during an opening operation of a compressed-gas circuit interrupter.

Another object of the present invention is to provide an improved synchronous-type compressed-gas circuit interrupter in which a highly efficient and effective outlet blast-valve means is utilized for the high-pressure interrupting chamber.

Still a further object of thepresent invention is to provide an improved synchronous-type compressed-gas circuit interrupter in which the high-pressure interrupting chamber constitutes the sole high-pressure storage reservoir for the interrupter.

In the US. patent application filed December 20, 1962, Serial No. 246,231, now US. Patent 3,215,797, issued November 2, 1965 to Fritz Kesselring, Ernst Gisiger and Lu=tz Seguin, there is disclosed and claimed a novel type of synchronous circuit interrupter utilizing compressed-gas as the arc-extinguishing medium. In the synchronous-type compressed gas circuit interrupter set forth in the aforesaid patent, means are provided to effect contact separation only during a point on the descending portion of the alternating-current wave, say, for example, approximately 2 milliseconds prior to a current zero with relation to SO-cycle-per-second frequency. It is a further object of the present invention to improve upon the synchronous-type compressed-gas circuit interrupter of the aforesaid patent rendering the exhaust-valve means for the interrupting chamber therefor of simplified construction, and providing a simplified pneumatic control therefor.

It has been discovered that synchronous-type circuit interrupters require only relatively small quantites of arc-extinguishing gas for extinguishing the arc, even during the interruption of high current values. In accordance with an important feature of the present invention, in the case of a synchronous-type compressed-gas circuit interrupter, the interrupting chamber itself is used as the only high-pressure interrupting gas reservoir.

Synchronous-type circuit interrupters require only a relatively small quantity of gas for extinguishing the are. For example, in single-phase circuit breakers an arcing time of 5 milliseconds is satisfactory. However, it must be taken into account that especially in polyphase synchronous breakers an instantaneous 'reclosure is necessary 3,253,107 Patented May 24, 1966 'ice in the case of an unsuccessful synchronized interruption, or in the case of a transient fault. It is, therefore, desirable to provide a time to account for all interruptions, say an arcing time of 2 to 3 half cycles, on' the basis of a SO-cycle-per-second frequency, thus allowing for an arcing time of 20 to 30 milliseconds. Experiments have shown that a 10 kv. synchronous circuit breaker adaptable for an interrupting rating of 500 mva. requires under such conditions approximately one standard liter of interrupting gas per each interrupting gap, and for each interruption. In the case of a high-pressure container having a volume of three liters, the pressure after each interruption is reduced only about 4 to 5%, so that after three interru-ptions in succession, the pressure drops, for example, from 8 atmospheres pressure to 7 atmospheres pressure without the admission of additional compressed gas.

The present invention is particularly concerned with a synchronized circuit breaker in which are extinction is achieved by the utilization of compressed gas, and in which the knowledge that the quantity of arc-extinguishing gas in synchronous-type circuit breakers is extraordinarily small is put into effect in a constructionally simple and economically advantageous manner. The circuit breaker of the present invention is distinguished, in part, by the fact that a part of the interrupting chamber is sealed off by a sealing-off valve member in the open or closed-circuit positions of the interrupter. Additionally, the invention is characterized by the fact that the interrupting chamber constitutes the sole high-pressu-re container for the arc-extinguishing gas. Another feature of the present invention relates to the fact that upon release of an interlock, the sealing-off valve member opens and is automatically thereafter closed again, following an adjustable period of time by means of a pneumatic device, or motor, operated by the arc-quenching gas.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in Which:

FIGURE 1 is a vertical sectional view taken through a synchronous-type compressed-gas circuit interrupter embodying the principles of the present invention, with the contact shown in the closed-circuit position; and,

FIG. 2 is a fragmentary sectional view taken substantially along the line IIII of FIG. 1.

Referring to the drawings, and more particularly to FIG. 1 thereof, the reference numeral 1 generally designates a synchronous-type circuit interrupter which is of the type set forth in the aforesaid patent application of Kesselring et al. Generally, the synchronuos-type circuit interrupter 1 includes an arc-extinguishing section 2, an operating system 3 and a control system 4. The arc-extinguishing section, or system 2, generally includes a relatively stationary orifice contact 5, through which a gas blast may flow, and a cooperable movable contact 6. As shown, the movable contact 6 is fixedly secured to the upper end of an operating rod 7, having secured to the lower end thereof an abutment 8, which, in turn, serves as the lower seat for an accelerating compression spring 9.- As a result, the accelerating compression spring 9 biases the movable contact 6 downwardly toward an opencircuit position away from the stationary contact 5. As well-known by those skilled in the art, the separation of the main contacts 5, 6 will effect the drawing of an are through the nozzle 10 associated with an orifice member 11 disposed in the upper end of a generally cylindricaltype casing 12 having a line terminal connection 13 at its upper extremity. The line terminal connection 13 is preferably made an integral part of an arcing electrode 14, to which the upper terminal of the established arc may terminate during the opening operation.

Controlling the upward flow of an arc-extinguishing blast of gas from the high-pressure region to a generally low pressure region 16 is a laterally-movable blast valve 17. The blast valve 17 is pivotally connected, as at 17a, to a crank-arm 17b, the latter being rotatable by means of an insulating longitudinally-extending valve operating rod 17c. The valve rod 170 as shown, extends, by way of a sealing connection 17d, exteriorly of the interrupting casing 12, and has fixedly secured thereto an externally-disposed crank-arm 172. The external end of the crank-arm 17e is pivotally connected to a valveactuating rod R latched, in the closed-circuit position, as shown, by an interlock L having a release coil 109. One end of the operating rod R is secured to the piston P of a pneumatic motor 0 comprising an operating cylinder 110.with the pistonP spring-biased'therein toward a valve opening position by a spring 111.

Upon release of the interlock L, as more fully described hereinafter, the compression accelerating spring 111 will eifect blast-valve opening movement of the piston P to the other end. of the operating cylinder 110. Stop means 115 including a ball 116 and a biasing compression spring 117 resiliently latches the piston P in the blast-valve opening position.

As shown, a normally-closed inlet .valve 120 is provided toward the valve-closing end of the operating cylinder 110. A high-pressure connection 125 extends from this end of the operating cylinder 110 to the arcing chamber 12. Additionally, a compressor 126 pneumatically connects with the high-pressure connection 125 and serves the function of compressing relatively low-pressure gas from the low-pressure storage reservoir 130 to recompress this gas to the higher pressure level adequate for storage within the high-pressure chamber 12, which constitutes the sole high-pressure storage reservoir of the interrupter 1.

As set forth in the aforesaid patent application, to effect contact opening movement, preferably there is provided an armature 32, to the lower end ofwhich is likewise fixedly secured to an operating rod 33; The operating rod 33 is pivotally connected at its lower extremity to an operating bell-crank 34, as at-thepivotal connection 35.

The operating bell-crank 34 is pivotally mounted upon a stationary pivot 36, and has one arm 37 pivotally connected, as by a pin-and-slot connection 38, toa rod end 39. The rod end 39 is fixedly, secured to the left-hand end of a trip rod 40, as viewed in FIG. 1.

. As shown in FIG. 1, the insulatingtrip rod 40 passes laterally through the interrupter casing 12 into aboss portion 12a thereof, andhasv a washer abutment 41 fixedly secured thereto to constitute the left hand seat of a compression spring 42. As shown, the compression spring 42 encircles the trip rod 40, and has its right-hand end bearing upon the lower extremity 43 of a latch 44 having an armature portion 45 secured thereto. The armature portion 45 is, at times, attractedto a holding magnet 46, which encircles a control circuit 47, which includes a movable control armature bar 48.

It will be noted that the movable control armature bar 48 is pivotally connected, as at 49, to an electro-dynamic magnet system 50 which encircles a main conductor stud 51, which terminates in a lower line terminal portion 52. A second line conductorL may be affixed to the lower terminal'52 of the interrupter 1, and the current passage through the interrupter 1 preferably comprises line conductor 52, main conductor stud'51, bracket portion 53, valve seat plate 54, the walls of an expansion chamber 56 associated with an operating cylinder 57, and through an upstanding cylindrical spring enclosure 58, encircling accelerating compression spring 9, and also constituting a main conductor portion of the interrupter.

To electrically carry the current between the movable main contact 6 and the cylindrical spring housing 58, there is preferably provided a plurality of circumferentially-disposed contact fingers 59, encircled by a garter tension spring 60, and biased radially inwardly into good contasting engagement between an upper recess portion 61 of line conductor 58, and rollers 62 interposed between the upper ends 59a of contact fingers 59 and the sides of the movable main contact 6. 4 z

The operating system 3, in addition, includes an operating piston 63 fixedly secured, as by a pin connection 64, adjacent the lower end of operating rod 7. A compression spring 65 encircles the lower operating rodpoftion 7a and abuts a slidable ring 66, which, at times, makes abutting engagement with a blast valve 67 fixedly secured to, and operated by, an operating valve lever 68. The valve lever 68 is pivotally mounted upon a stationary pivot 69. The pivot 69, in addition, serves as a pivot for the aforementioned latch lever 44.

A pin 70, passing laterally through the lower end 7a of the operating rod 7, picks up the operating valve 67 toward the end of the closing operation of the movable contact 6.

The casing 12 includes an upper insulating closure member 71, a lower closure member 72, and interiorlydisposed suitably-configured insulating spacing sleeves 73, 74 and 75. As shown, the spacing sleeves 74 and 75 have longitudinal bores 76 provided therethrough to form interconnecting conduits interconnecting the low-pressure region 16- with the region 77 interiorly of the expansion chamber 56.

In the particular embodiment of the invention shown, there is provided a recirculating gas system 78, whereby a relatively effective arc-extinguishing gas, such as sulfur hexafiuoride (SP gas, is utilized as the arc-extinguishing gas.

It will be noted that the whole of the interrupting casing 12 below the blast valve 17 is at relatively high pressure, whereas the region 16 above the blast valve 17 and the region 77, interiorlyof the expansion chamber 56, and above the valve 67, is at relatively low pressure.

In the closed-circuit position of the circuit interrupter 1, as illustrated in FIG. 1, it will be apparent that the main current path through the interrupter includes line connection L line terminal 13, spider support for supporting arcing electrode 14, spider members 85a, orifice. member 11, relatively stationary fingers 5, movable contact 6, rollers 62, bridging fingers 59, mainconductor 58, operating cylinder 57, valve plate 54, bracket portion 53, lower main conductor 51, to line terminal 52.to line conductor L As shown in FIG. 1, in the closed-circuit position of the interrupter 1, the interrupter is held in the closed position by the latches 44, 68 and the trip bar 40. If the interrupter 1 is to be opened, then first the tripping coil 86 and the interlock release coil 109 are energized, in an impulse like manner, as, for example, by the discharge of a suitable associated capacitor. However, as shown, a protective relay 86a, responsive to the fault current in the.

line L or a manual trip button 865 may be used to .energize the tripping coil 86 and the release coil 109. from sources of energy 100, 101. This results in a downward movement of the armature 32 and rotation of the operating bell-crank 34. After traveling through the length of the pin-and-slot connection 38, the. insulatingoperating trip bar 40 moves to the left, and causes release of the latch 44, whereby the opening sequence is initiated;

The energization of the release coili109 releases the interlock. L and permits the spring. 1111to force the piston P to the left, as viewed in FIG. 1 opening the blastvalve 17 through the associated linkage 17c untilthe stop ball 116. falls in.

It will be assumed that the main, and therefore also the control current, are so small in magnitude that the aramature 45 of the holding magnet 46 is not held against the force of the compression spring 87. The accelerating spring 9 will consequently force the movable contact 6 downwardly and unplugv the orifice 10, to permit the gas blast to extinguish the established arc.

However, at the same time, the adjusting screw 109 strikes the valve disc 120, whereafter the quenching gas flows into the cylinder 110 either from the small pres sure space of the compressor 126 or from the interrupting chamber 12. As soon as the pressure under the piston P has reached such value that the forces produced by the stop 115 and the spring 111 are overcome, the piston P is moved with considerable speed again to its rightward position, as viewed in FIG. 1, whereby the valve slide 17 is reclosed, as shown in FIG. 1. When the pressure in the low pressure container 130 reaches, for example, two atmospheres gauge pressure, then the compressor 126 starts into operation and brings the interrupting chamber 12 again to a pressure of approximately 8 atmospheres gauge pressure. It can be seen, that in case of the disclosed arrangement, a separate high-pressure tank is no longer necessary, and the opening and closing of the valve slide 17, by means of which the interrupting chamber 15 is sealed in a gas-tight manner in the closed and open positions, is obtained in a simple way by the extinguishing gas itself.

However, during the occurrence of relatively large currents, for example, approximately twice the nominal, or load current, and particularly during the occurrence of short-circuit currents, the synchronized control 4 will at this time come into play in the following manner: When the impulse to trip is given, again the tripping coils 86 and 109 are energized at any arbitrary instant on the current wave, and the blast valve 17 is withdrawn laterally to open the nozzle exhaust in the manner previously described. The tripping bar 40 is moved to the left, and the main current flowing through the interrupter 1 is changing as a function of time. The main current flow through the main conductor 58 causes a flex change in the magnetic system 88. At the same time, there appears between the points A and B an ohmic voltage drop. In order to produce an ohmic voltage drop of sufficiently high value without reducing the cross-sectional area of the conductor 58 too much, it may be of advantage to make the main conductor 58 and the operating cylinder 57 of a material having a resistivity higher than that of copper, for example, of brass or of bronze.

In the closed-circuit starting with point A, along the line 47 leading through the holding magnetic system 46, through the movable conductor 48 up to the point B and back through the operating cylinder 57 and the main conductor 58 to the point A, there is produced, partly due to the change of flux in the magnetic system 88 and partly due to the ohmic voltage drop mainly in the main conductor 58, a resultant voltage, which forces through the mentioned loop circuit the control current i This control current i energizes the holding magnet 46 and results in that despite the withdrawing of the trip bar 40, nevertheless the synchronized break 1 will not start the opening, or tripping movement immediately, but only when the control current i falls below a predetermined value, at which time the armature 45 releases under the effect of the compression spring 87. When this occurs, the latch 44 is released without any time delay, that is instantaneously.

It will be apparent that latching means 44 for latching the separable contacts 5, 6 in their closed position is released by an'actuated condition of a first mechanical release operator 40 and a second release timing operator 46, energized by a phase-shifted current 1' with respect to the main circuit current i The control current i passes in the secondary circuit 47, which includes the rotatable control armature 48, a part of the electrodynamic system 50.

The reclosing valve 67, valve lever 68 and prop latch 48 constitute a reclosing operator 99, which functions during unsuccessful synchronous operations, to reclose the separated contact structure 5, 6 and wait for a time close to the next current zero for the latching means 44 to again function. Such opening and reclosing may continue until the circuit is interrupted, thereby conserving are energy.

The essence of the synchronized control 4 then consists in that this minimum value of the control current i is reached, for example, approximately 2 milliseconds before the main circuit current passes through its zero value, which can be obtained through a suitable choice of the inductive and ohmic components of the secondary circuit 47, while taking into consideration the saturation phenomena in the magnetic system 88. As long as interruption takes place, that is, as long asthe arc remains extinguished at the time of the main circuit current passing through its zero value, the breaker 1 will remain in the open position.

It is true that the compression spring 65 encircling the operating rod exerts pressure upon the reclosing value disc 67, but this is latched closed through the latch lever 68, and also by the pivotal movable control conductor 48, so that the reclosing valve 67 can not open.

If the circuit interrupter- 1 is to be closed, then either the left-hand end of the trip bar 40 is mechanically moved in the direction indicated by the arrow 90, or else the closing coil 91 is energized by a closing button 910 so that the armature 32 is drawn upwardly. By movement of the tripping bar 40 to the right, as viewed in FIG. 1, the movable control conductor 48 is rotated from the illustrated position of FIG. 1 clockwise, whereupon the operating latch lever 68 is released, and the closing valve 67 is opened under the effect of the compression spring 65 encircling the lower portion 7a of the operating rod 7.

When this occurs, the high-pressure gas within the region 15 flows upwardly into the operating cylinder 57 to act upon the lower surface of the operating piston 63. This will effect upward closing movement of the movable main contact 6 and effect reengagement of the main contact 5, 6. Toward the end of the closing operation, the pin 70 secured to, and movable with, the operating rod portion 7a will reengage the closing valve 67, and carry the operating valve 67 to its closed position, as shown in FIG. 1 in which position it is again latched.

If, for any reason, the arc-extinguishing action at current zero does not take place, or if during an interrupting operation of a smaller current magnitude there occurs a so-called transient fault, then movable conductor 48 is rotated in a clockwise direction about its pivotal support 49 by a large force under the effect of the considerable magnetic flux present within the air gap 93 (FIG. 2) of the electrodynamic magnet system 50. When this occurs, the reclosing valve 67 is released in the same manner as in the case of a manual closing operation. As a result, it is of considerable importance that in the air gap 93 (FIG. 2) there occurs at approximately double nominal current maximum induction B of at least 15,000 gauss, and that at the same time the control current i has a very high value. As well-known by those skilled in the art, electrodynamic force which results is in accordance with the formula:

where L is equal to the active length of the conductor 48. The large force F in Equation 1 results in the release of the reclosing valve 67 in a fraction of a millisecond. After being released, the valve 67 can move downwardly as a result of compression of gases below the piston 63, which compression is, under certain circumstances, supported also by the effect of the spring 65. As a result, instantaneous reclosing will take place in opposition to the effect of accelerating compression spring 9 in a time of 1 to 2 milliseconds Immediately after a reclosing operation, the latch 94 returns to its latching position under the effect of the tension spring 95 back into the position illustrated in FIG. 1 of the drawings. As a result of the effect of the large magnitude control current i produced by the continued flowing main current, the armature 45, and with it the latch 44 is again attracted to the holding magnet 46. In addition, the movable pivotal control conductor 48 returns to the position illustrated in FIG. 1 under the effect of the compression spring 92, so that the circuit interrupter 1 is ready for another synchronous opening operation just prior to the next passage of the main circuit current through its zero value.

It will be observed that in the closed-circuit position of the circuit interrupter 1, as illustrated in FIG. 1 of the drawings, instantaneous exhaust of the operating cylinder 57 occurs through the exhaust openings 96 when the operating piston 63 is in its contact-closed or upper position As shown, the exhaust openings 96 lead into the expansion space 56, which leads, in turn, by way of the conduits 76, to the low-pressure region'16 of the interrupter 1. It is very important for rapid exhausting of the region 97 below the operating piston 63 that the expansion space 56 be connected with the operating cylinder 57 directly, and through the shortest possible exhaust pipe connections, which, preferably, may assume the form of the exhaust openings 96. As a result, the exhausting of the gas from the region 97 may occur in a time of approximately 1 millisecond.

The occurrence of a transient fault condition during a load opening operation will result in, the movable control conductor 48 rotating clockwise with considerable force in exactly the same manner, whereupon an instantaneous reclosing operation follows. Shortly before the next passage of the main circuit current through its zero value, a synchronized tripping interruption takes place in the previously described manner.

From the foregoing description it will be apparent that there is provided an improved synchronous-type compressed-gas circuit interrupter in which considerable advantage is obtained from the knowledge that only a small quantity of arc-extinguishing gas is utilized for each opening operation. In addition, it will be apparent that a simplified and highly effective pneumatic control for the blast valve 17 is provided. Adjustability is readily obtained by the structure shown. It will be noted that the arc-extinction and reclosing energy is obtained from the same source of compressed gas disposed within the interrupting chamber 12. Moreover, it will be noted that the magnitude of the energy consumed during an interrupting operation is relatively low due to the fact that the contacts are separated only near a current zero during large magnitude currents of fault magnitude. Finally, it will be apparent that the circuit interrupter 1 is of relatively small dimensions and composed of relatively few parts.

The blast-valve operating structure has been illustrated in connection with a synchronous-type compressed-gas circuit interrupter of small dimensions. However, it will be apparent to those skilled in the art that such a blastvalve operating arrangement for momentary opening and adjustable closing may be applicable to other types of compressed-gas circuit interrupters rather than merely the synchronous-type.

Although there has been illustrated and described a specific structure, it is to be clearly understood that the same was merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the invention.

I claim as my invention:

1. In a synchronous-type gas-blast circuit interrupter having a pair of separable contacts adapted to open a predetermined time prior to a current zero in the main circuit current being interrupted, the combination therewith of a high-pressure interrupting chamber which constitutes the sole high-pressure gas supply, a sealing valve member for closing the outlet of the sole high-pressure chamber in the closed and in the fully open-circuit position of the interrupter, a pneumatic motor for actuating said sealing valve member to the open and closed positions, means defining an interlock for preventing the actuation of the pneumatic motor until the initiation of an arc-extinguishing operation, and adjustable means associated with said pneumatic motor for causing a delayed closing of said sealing valve member.

2. In a synchronous-type gas-blast circuit interrupter having a pair of separable contacts adapted to open a predetermined time prior to a curent zero in the main circuit current being interrupted, the combination therewith of a high-pressure interrupting chamber which constitutes the sole high-pressure gas supply, a sealing valve member for closing the outlet of the sole high-pressure chamber in the closed and in the fully open-circuit position of the interrupter, a pneumatic motor for actuating said sealing valve member to the open and closed positions, said pneumatic motor including an operating cylinder and an operating piston movable therein, normally-closed Valve means disposed at the end of said operating cylinder toward which the piston moves upon sealing valve opening, a high-pressure connection between the high-pressure interrupting chamber and the back side of said normally-closed valve means, means defining an interlock for preventing the actuation of the pneumatic motor until the initiation of an arc-extinguishing operation, and adjustable means associated with said pneumatic motor for causing a delayed closing of said sealing valve member.

3. The combination of claim 2, wherein the adjustable means includes an adjustable abutment movable with the operating piston for striking the normally-closed valve means and effecting thereby the opening of the same.

4. The combination of claim 3, wherein stop means are provided toward said end of the operating cylinder which may be forced to a released position upon the attainment of suflicient pressure by opening of said normally-closed valve means.

5. A gas-blast circuit interrupter including an orificetype relatively stationary contact and a movable contact cooperable therewith, means defining an outlet chamber, a high pressure inlet chamber and normally closed valve means therebetween, a pneumaticmotor for said valve means including an operating cylinder and a piston movable therein, interlock means for latching operative movement of said piston, normally closed inlet valve means associated with the closing end of said operating cylinder,

and abutment means movable with the piston to effect No references cited.

KATHLEEN H. CLAFFY, Primary Examiner. 

1. IN A SYNCHRONOUS-TYPE GAS-BLAST CIRCUIT INTERRUPTER HAVING A PAIR OF SEPARABLE CONTACTS ADAPTED TO OPEN A PREDETERMINED TIME PRIOR TO A CURRENT ZERO IN THE MAIN CIRCUIT CURRENT BEING INTERRUPTED, THE COMBINATION THEREWITH OF A HIGH-PRESSURE INTERRUPTING CHAMBER WHICH CONSTITUTES THE SOLE HIGH-PRESSURE GAS SUPPLY, A SEALING VALVE MEMBER FOR CLOSING THE OUTLET OF THE SOLE HIGH-PRESSURE CHAMBER IN THE CLOSED AND IN THE FULLY OPEN-CIRCUIT POSITION OF THE INTERRUPTER, A PNEUMATIC MOTOR FOR ACTUATING SAID SEALING VALVE MEMBER TO THE OPEN AND CLOSED POSITIONS, MEANS DIFINING AN INTERLOCK FOR PREVENTING THE ACTUATION OF THE PNEUMATIC MOTOR UNTIL THE INITIATION OF AN ARC-EXTINGUISH- 